Siemens S7-1200 System Manual page 563

I-device without lower-level PROFINET IO system
The I-device does not have its own distributed I/O. The configuration and parameter
assignment of the I-devices in the role of an IO device is the same as for a distributed I/O
system (for example, ET 200).
I-device with lower-level PROFINET IO system
Depending on the configuration, an I-device can also be an IO controller on a PROFINET
interface in addition to having the role of an IO device.
This means that the I-device can be part of a higher-level IO system through its PROFINET
interface and as an IO controller can support its own lower-level IO system.
The lower-level IO system can, in turn, contain I-devices (see figure below). This makes
hierarchically structured IO systems possible.
In addition to its role as IO controller, an I-device can also be used through a PROFIBUS
interface as DP master for a lower-level PROFIBUS system.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Communication
10.2 PROFINET
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